This invention relates to finned tubing. The invention relates in particular to a method of manufacturing finned tubing from tubular metal fin stock, to apparatus for manufacturing finned tubing and to finned tubing manufactured in accordance with the method.
More specifically the invention relates to the manufacture of finned tubing by employing a plurality of rollers drivably mounted on arbors spaced about the tubular fin stock. Each of the rollers includes a plurality of axially arranged forming discs, the arrangement being such that the discs on the respective rollers track with each other. The discs can be brought into rolling contact with the fin stock and when this is done and the arbors are driven, the discs penetrate into the fin stock and deform the stock so that the metal in the fin stock is forced into axial spaces between the forming discs to thereby form fins on the fin stock. The axes of the arbors intersect the axis of the fin stock so that when the arbors are driven the forming discs traverse the fin stock longitudinally and thereby extrude helical fins from the fin stock.
According to the invention there is provided a method of manufacturing finned tubing from tubular metal fin stock which includes providing the fin stock in axially continuous form and providing on the fin stock at least two finned regions and at least one finless region interposed between two finned regions.
The metal fin stock may be provided in one piece or it may be in separate parts which are secured to each other so as to be axially continuous. The securing together may for example be by welding.
The method may include forming the tubing in linear form with the finned and the finless regions longitudinally spaced from each other.
The method may further include employing a plurality of rollers drivably mounted on arbors spaced about the tubular fin stock, each of the rollers including a plurality of axially arranged forming discs which can be brought into rolling contact with the fin stock and the rotational axis of each arbor intersecting the longitudinal axis of the fin stock.
Still further the method may include intermittently engaging the forming discs with the tubular metal fin stock and disengaging the forming discs from the fin stock. This arrangement may include engaging the forming discs with the fin stock to thereby form fins and thus a finned region in the fin stock, disengaging the forming discs from the fin stock, axially advancing the metal fin stock so that a finless region is provided on the fin stock, and reengaging the forming discs with the fin stock to again form fins and thus a finned region axially spaced from the first finned region by the finless region.
The fin in the finned region may be developed to its full height over an axial distance of the fin stock equal to from 0:40 to 0:75 of the outside diameter of the fully developed fin, and more specifically over an axial distance of the fin stock equal to from 0:50 to 0:60 of the outside diameter of the fully developed fin.
The method may further include effecting relative rotation in one direction of the discs with respect to the tubular fin stock, bringing the discs into rolling contact with the tubular fin stock at a position intermediate the ends of the fin stock and developing a helical fin extending over a finite axial distance of the fin stock, arresting the rotation of the discs and reversing the direction of rotation of the forming discs so that the axial displacement of the fin is thereby reversed. This method may include maintaining the reverse axial displacement of the fin stock until the axial starting point of the fin generation is reached and then continuing the rotation of the forming discs and the axial displacement of the fin stock past the starting point, and generating the fin over a finite axial distance of the fin stock extending beyond the starting point.
Conveniently, the method may include controlling the bringing of the forming discs into rolling contact with the tubular fin stock during oscillating reversal of the direction of rotation of the forming discs.
One method of control may include closing the arbors continuously on the fin stock during oscillating reversal of direction of rotation of the forming discs.
Another method of control may include closing the arbors in stages on the fin stock during oscillating reversal of rotation of the forming discs.
The reversing of the direction of rotation of the forming discs may be effected substantially instantaneously.
Relative rotation between the forming discs and the fin stock may be effected by drivingly rotating the forming discs and imparting contra-rotation to the fin stock due to frictional engagement of the discs with the fin stock.
The forming of the finned regions may be started approximately in the axial central region of the fin stock and further finned regions may then be formed from the central region outwardly towards the end regions of the tube.
The forming discs on the different arbors conveniently track each other and engage the fin to a different extent to facilitate rapid development of the fin to its full height. One forming disc on one arbor may engages one third of the height of the fin, the tracking forming disc on a second arbor may engage a further third of the height of a fin, and a tracking forming disc on a third arbor may engage the final third of the height of the fin.
The method may particularly include bringing the forming discs into rolling contact with the fin stock by closing the forming discs around the fin stock by moving them in a radial direction towards the fin stock, forming an axial length of fin by rotation of the forming discs, arresting the rotation of the discs to terminate the fin, reversing the direction of rotation of the forming discs substantially instantaneously to thereby displace the fin in an opposite axial direction, and when the forming discs reach the axial starting point of the formation of the fin, closing the forming discs around the fin stock to thereby develop the fin in an axially opposite direction from the starting direction.
The axial transition from the finned to the under developed finned region may be effected by oscillatingly reversing the rotation of the discs a few revolutions.
The fin formation may be continued for a desired axial length and the discs may then be released from the fin stock to thereby terminate the fin.
The rotational axes of the arbors may intersect the axis of the fin stock at different angles.
The method may further include crushing an axial region of under developed fins blending from a region of fully developed fins to a finless region so that thereby an abrupt transition is made from a region of fully developed fins to a finless region. The under developed fins may be crushed to have a cross-sectional dimension which is uniform with and which blends into the finless region.
An alternative method may include forming at least a part of the finless region by machining away fins from a finned region. The finned tubing may be bi-metal comprising a tubular metal fin stock on a tubular metal liner.
Further according to the invention there is provided apparatus for manufacturing finned tubing from tubular metal fin stock in which the tubing has finned and finless regions, the apparatus including three rotatably drivable arbors, a plurality of axially arranged forming discs mounted on each arbor to be rotatably drivable by the arbors, the forming discs on the arbors being arranged to track each other in axially spaced groups, and the diameters of the forming discs in each tracking group on the arbors having different diameters.
The diameters of the tracking forming discs in each tracking group may vary in the proportion 1 to 1:1 to 1:2.
The axis of each arbor may intersect the longitudinal axis of the fin stock, and the rotational axes of the arbors may intersect the longitudinal axis of the fin stock at different angles.
The angle of intersection between the rotational axis of each arbor and the longitudinal axis of the fin stock may be between 3 degrees and 7 degrees. Specifically, the angles of intersection between the rotational axes of the arbors and the longitudinal axis of the fin stock may be 3 degrees for one arbor, 4 degrees for another arbor and 6 degrees for the third arbor.
The set of forming discs on each arbor may include discs of different diameters. The axial length of the set of forming discs on each arbor may be shorter than the overall diameter of the largest discs in each set. The overall diameter of the largest discs on each arbor to the length of the set of discs is in the ratio of from 2:2 to 1 to 2:6 to 1.
The forming discs on each arbor may be provided in three axial regions, a first axial region including discs of different diameters with the axially extending profile of the discs tapering axially, a second axial region similar to the first axial region including discs of different diameters but with the axially extending profile of the discs tapering axially in an opposite direction, and a third axial region of discs of equal diameter interposed between the first and the second axial regions. The first and the second axial regions may each include four forming discs and the third axial region may include six forming discs.
The axial spacing between the forming discs in the axially tapering first and second regions may be different from the axial spacing between the forming discs in the third axial region.
Conveniently, the direction of rotation of the arbors may be reversible.
Still further according to the invention there is provided finned tubing formed from continuous tubular metal finned stock which includes at least two finned regions and at least one finless region interposed between the finned regions. At least one finned region may include an axial region in which the fin is only partly developed, and an axial region in which the fin is fully developed, the axial length of the under developed finned region being from 0:50 to 0:60 of the diameter of the fully developed fin.
Finned tubing according to the invention may be bi-metal including tubular metal fin stock on a tubular metal liner.
The invention further extends to bi-metal finned tubing whenever manufactured in accordance with the method of the invention.